Cloudflare + FritzBox -> DynDNS

updateDns.php

<?php
/*
FRITZ!Box DynDNS Howto:
Update-URL:	http://your-domain.tld/filename.php?user=<username>&pass=<pass>&hostname=<domain>&myip=<ipaddr>
Domainname:	dyndns.your-domain.tld
Username:	your-cloudflare-email-address
Password:	your-cloudflare-api-token
*/

// static config:
$cfZoneId =	""; //put your CloudFlare Zone ID here
$cfDnsId =	""; // put your CloudFlare DNS Identifier here

// dynamic config
$cfEmail =	$_GET['user'];
$cfApikey =	$_GET['pass']; 
$updateDomain =	$_GET['hostname'];
$ipAddr =	$_GET['myip'];

$cfUrl =	"https://api.cloudflare.com/client/v4/zones/".$cfZoneId."/dns_records/".$cfDnsId;

$data = array(
  "type" => "A",
  "name" => "{$updateDomain}",
  "content" => "{$ipAddr}",
  "ttl" => 120,
  "proxied" => false,
  );

$curl = curl_init($cfUrl);

curl_setopt($curl, CURLOPT_CUSTOMREQUEST, "PUT");
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, array('Content-Type: application/json',"X-Auth-Email: $cfEmail","X-Auth-Key: $cfApikey"));
curl_setopt($curl, CURLOPT_POSTFIELDS, json_encode($data));


$response = curl_exec($curl);
if (!$response) {
    die("Connection failure.");
}else{
	var_dump($response);
}

?>

Although this script isn't really maintained and in use anymore, vou can actually run in wherever you want, as long as there's PHP and curl available. The FRITZ!Box itself has to be configured to a custom DynDNS Provider, pointing to the url where this script is located. That can be on a RPI or a shared webhosting, as long as it's reachable for your FRITZ!Box. There's no cron needed, as the FRITZ!Box automatically fires a request as soon as a new IP is assigned or the box is rebooted.

Additionally, see the forks of this script which seemingly have been updated to an easier-to-understand version. I actually uploaded this gist almost 4 years ago just to have it saved somewhere, not knewing that this might be used somewhere else :P

Example FRITZ!Box Configuration: https://img.doxylamin.pro/2020-06-07/gdu5yOZpNb.png
I've initially made the username and password to cloudflare email & api token just to have some kind of "security" so not everyone who knows the path of the script can override the DNS entry.